Treatment of metals



Dec. 30, 1947. w. M. ROBERDS TREATMENT OF METALS Filed May 21, 1945GINA-E0703 (Ittorneg Patented Dec. 30, 1947 TREATMENT OF METALS WesleyM. Roberds, Collingswood, N. J., assignor to Radio Corporation ofAmerica, a corporation of Delaware Application May 21, 1943, Serial No.487,942

3 Claims.

This invention relates to the heat treatment of metals, and moreparticularly to a method of and means for rendering the metal suitablefor a hardening treatment with the aid of heat induced by high frequencycurrents.

The use of ferrous metal parts in many industrial applications and otherfields of use is very well known. Where such parts involve surfaceswhich rub against each other, as in the case of the bearing surfaces ofconnecting rods which are in engagement with crank shafts of internalcombustion engines, for example, these surfaces are subject toconsiderable wear. In order to prolong the lifeof the parts involved, ithas been necessary to harden the surfaces.

In the copending application of George H. Brown, Serial No. 421,746, nowPatent 2,424,794, assigned to Radio Corporation of America, there isdisclosed a method of hardening various metals by the use of highfrequency electrical energy at sufficiently high power to obtainextremely rapid heating of the work along only a relatively thin layerunder the surface to be hardened, and thereafter permitting the heat tobe dissipated through the metal which backs up the heated layer at arate which is of the order of the rate at which the heat is applied. Theheated work thus undergoes self-quenching, so to speak.

Where the work is of substantial thickness, the portion thereof in backof the thin, heated layer is ordinarily adequate to conduct away theheat with sufficient rapidity. In some instances, however, the work isvery thin, and it becomes necessary to back up the work with arelatively thick material of high conductivity in order to provide therequisite backing to permit selfquenching. For this purpose, Brown hasproposed backing up the work with a relatively low melting point metal,such as Woods metal or solder. This is, of course, feasible only wherethe surface to be hardened is surrounded by a hollow enclosure as, forexample, in the case of hollow engine block u ed in airplanes. Here, thecylinder bores are surrounded by hollow enclosures into which the lowmelting point metal can be poured and from which it can be permitted torun out when it melts while the heat developed in the block by the radiofrequency energy treatment is dissipated therethrough. In a great manyinstances, however, there is no such hollow enclosure which can befilled with the low melting point backing metal, and therefore theproposal made by Brown is inapplicable.

The primary object of my present invention is to provide a method of andmeans for backing up the work to be treated in cases where the methodproposed by Brown is not feasible.

More particularly, it is an object of my present invention to provide animproved method of and means for backing up thin-walled metals onesurface of which is to be hardened, which method and means areapplicable in cases where the thin-walled metal is not surrounded by ahollow enclosure or the like in which a low melting point backing metalmay be placed.

Another object of my present invention is to provide a method of andmeans for backing up metal as aforesaid which can be practiced andutilized even by one not skilled in the art, which are inexpensive incost, and which are highly efiicient in use.

In accordance with my present invention, I apply to that surface of themetal which is not to be hardened a solid backing material of requisitethickness and of a character such that it can be forced into intimatecontact with such surface. The backing material should, of course, beone which is highly heat conductive, and for this purpose a metallicbacking member is preferably employed. Thus, for example, if the outersurface of a cylindrical, metallic member is to be hardened, there maybe employed an expansible bolt or core which is placed within thecylindrical. member, and the core or bolt expanded to make intimatecontact with the inner wall of the cylindrical member. The outer wallthereof may then be scanned by a suitable applicator to which radiofrequency energy is supplied and which will induce in the work a currentfor heating the outer surface thereof. If the work is heated rapidly inthe manner taught by Brown, only a very thin layer under the outersurface of the work will be heated to the hardening temperature, and thebacking bolt, which is made thicker than the thickness of the wall ofthe cylinder-member, will conduct away the heat at substantially thesame rate as it is applied. Shouldit be desired to harden the innersurf-ace of the cylindrical member, then the outer surface thereof maybe backed up by a contractible sleeve which may be contracted intointimate contact with the outer surface of the work. In such case, theinner surface of the cylindrical member is suitably scanned as abovedescribed, and the heat developed in the work is rapidly dissipatedthrough the outer and relatively thick, backing member.

The novel feature that I consider characteristic of my invention are setforth with particularity in the appended claims. The invention itself,however, both as to its organization and method of operation, as well asadditional objects and advantages thereof, will best be understood fromthe following description when read in connection with the accompanyingdrawing, in which Figure 1 is a central, sectional view of a thinwalled,cylindrical member the outer surface of which is to be hardened and inconnection with which my present invention is employed for backing upthe wall thereof at the inner surface,

Figure 2 is a sectional view taken along, the plane of the line 11-11 ofFigure 1,

Figure 3 is a view similar to Figure 1 but showing the backing memberapplied to the outer surface of the cylindrical member in the case wherethe inner surface of the work is to be hardened,

Figure 4 is a side elevation of a connecting rod bearing in connectionwith which my present invention may be employed, and

Figure 5 is a plan view of the connecting rod bearing along the plane ofthe line VV of Figure 4.

Referring more particularly to the drawing, wherein similar referencecharacters designate corresponding parts throughout, there is shown,inFigs. 1 and 2, a cylindrical member I of ferrous metal or the like andthe outer surface of which is to be hardened. For this purpose, theremay be utilized a suitable applicator 3 in the form of an inductor whichis connected through a pair of leads 5 and a transformer 'I to a sourceof high frequency energy 9, such as a vacuum tube oscillation generator.The applicator 3 surrounds the work I in closely spaced relationthereto. Relative movement between the work I and the applicator 3 in adirection longitudinally of the member I may be effected in any suitablemanner whereby the work will be scanned by the applicator to effectheating of only a very thin, skin layer under the outer surface of themember I.

Within the hollow cylinder I, there is placed a radially eXpansible boltI I having a plurality of longitudinally spaced, circumferentiallydistributed slots I3 and a tapered bore I5. Within the tapered bore I5is a correspondingly tapered member I? which can be forced into the boreI5 by a nut lea threaded on the smaller, threaded end Ha thereof. A nutISb on the larger, threaded end Ilb of the tapered member I! may belater utilized for withdrawing the tapered member from the bolt I I.Forcing the tapered member Il into the bore I5 causes the bolt II toexpand radially outwardly into very intimate or snug engagement with theinner surface of the cylindrical member I. Thus, there is afforded athick, backing member I I, I! behind the unhardened, inner surface ofthe member I for rapidly conducting away from the member I the heatdeveioped in the thin, heated layer thereof under its outer surface, sothat the Work can be quickly self-quenched.

The expansible bolt I I and the wedge II should, of course, be made ofhighly heat conductive material and are preferably made of metal. Theslots I 3 may be milled or formed in any other suitable manner in thebolt II and preferably terminate at points short of each end of thebolt, as clearly shown in Figure 1. The number of slots I3 which arenecessary will vary with the type of work involved, and may vary fromtwo upwardly in number. In any case, the slots I3 should be narrowcompared to the thickness of the material between them, and the fewer innumber, the better, as this affords more area of contact between thebolt I I and the inner surface of the work I.

In Fig. 3, I have shown an arrangement for heating the inner surface ofthe cylindrical member I. For this purpose, there may be fitted onto theouter surface of the member I a contractible sleeve 2I provided withlongitudinally extending, circumferentially distributed slots 23 similarto the slots I3 of the expansible bolt II except that, in this case, theslots 23 extend clear to one end of the sleeve 23, as shown in Figure 3.After placing the sleeve 2| on the thin-walled cylinder I, one or moreclamping rings 25 of suitable internal diameter are force-fitted overthe sleeve 2I to contract it into intimate engagement with the outersurface of the cylindrical member I. The inner surface of the member Imay then be scanned by the applicator 3 as above described, and the heatdeveloped in the work I will be rapid'y dissipated through therelatively thick, backing member 2I to effect self quenching of thework.

In Fig. 4, I have shown my invention applied specifically to aconnecting rod 3I of the type used to connect a piston to the crankshaft of an internal combustion engine, and the bearing surface 3Ia ofwhich is to be hardened. The connecting rod 3| is provided with boltholes 33 which are so located that they are surrounded by Very thin Wallportions 35 adjacent the surface 3Ia of the connecting rod. To preventthe thin wall portions 35 from becoming overheated and warped orotherwise distorted, it is necessary to have the heat developed thereinconducted away rapidly. For this purpose, there may be inserted intoeach of the bolt holes 33 an expansible bolt arrangement such asdescribed above in connection with Figs. 1 and 2.

A yoke 31 of copper or the like provided with openings 39 adapted toregister with the openings 33 for the reception of the protruding endI'Ib and the nut 19b of the respective tapered members I1 is placedagainst the connecting rod 3| in the manner clearly shown in Fig. 4. Theyoke 31 completes the path for the high frequency current induced in therod 3I when the surface 3 la thereof is scanned by the applicator 3.Since the thin wall portions 35 are suitably backed up by the highlyheat conductive bolts II and the Wedges II, the heat developed thereinwill be rapidly conducted away therefrom to effect selfquenching, andwarping thereof will be minimized. In place of the yoke 31, it may bedesired to utilize the bearing cap (not shown) which normaliy cooperateswith the connecting rod 3I. However, the copper yoke 31 has been foundpreferable in practice since it makes better electrical contact with theconnecting rod 3| and assists in conductin away the heat from the thinwall portion 35, i

From the foregoing description, it will be apparent that I have provideda very simple means for and method of carrying out the teachings of theabove identified Brown application in cases where enclosures forreception of the backing metal around the work the surface of which isto be hardened are lacking. Although I have shown and described myinvention in connection with two specific applications, it will, nodoubt, be obvious to those skilled in the art that many otherapplications and modifications thereof are possible. Moreover, while Ihave described my invention primarily with reference to the hardening ofmetals, it should be apparent that it is equally applicable to theannealing of metals by a heat treatment. I therefore desire that myinvention shall not be limited except insofar as is made necessary bythe prior art and by the spirit of the appended claims.

I claim as my invention:

1. The method of altering the hardness of one wall surface of a hollow,thin-walled, ferrous metal member hardenable by heating and quenchingwhich comprises placing against the opposite wall surface of said membera relatively thick, second, metallic member of variable diameter, thenvarying the diameter of said second member to bring it into intimateengagement with said opposite surface whereby said second member willback up said first named member, then subjecting said one surface to theinfluence of a high frequency magnetic field of such intensity and forsuch a period of time as to induce in the region of said one surface acurrent which will rapidly heat only a very thin layer of said memberunder said one surface to a temperature requisite for hardening thereofwhile said members are maintained in intimate engagement with eachother, and finally permitting the heat developed in said heated layer tobe dissipated relatively rapidly substantially solely through saidsecond member.

2. The method set forth in claim 1 wherein said one surface is the outersurface of said thinwalled member, and wherein said second member is anexpansible member adapted to be expanded to be brought into intimateengagement with the inner surface of said thin-walled member when saidsecond member is placed therein.

3. The method of altering the hardness of one wall surface of a hollow,thin-walled, ferrous metal member hardenable by heating and quenchingwhich comprises placing against the opposite wall surface of said membera relatively thick, second, metallic member of variable diameter, thenvarying the diameter of said set:-

ond member to bring it into intimate engagement with said oppositesurface whereby said second member will back up said first named member,then continuously subjecting successive 5 portions of said one surfaceto the influence of a high frequency magnetic field of such intensityand for such a period of time as to induce in the region of said onesurface of each of said successive portions a current which will heatonly a very thin layer of said member under said one surface to atemperature requisite for hardening thereof while said members aremaintained in intimate engagement with each other, and finallypermitting the heat developed in the heated layer of said successiveportions to be dissipated relatively rapidly substantially solelythrough said second member.

WESLEY M. ROBERDS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,280,102 Somes Apr. 21, 1942308,639 Stevens Dec. 2, 1884 1,168,794 Enoch Jan. 18, 1916 1,648,032Starkin Nov. 8, 1927 1,249,532 Smith et a1 Dec. 11, 1917 455,420 ThomsonJuly 7, 1891 2,316,506 Doelker et a1 Apr. 13, 1943 153,115 Robinson July14, 1874 539,089 Simonds May 14, 1895 FOREIGN PATENTS Number CountryDate 668,820 France July 22, 1929 0 467,308 Great Britain June 5, 1937OTHER REFERENCES Metals Handbook, 1936 ed., page 94; ibid., 1939 ed.,page 329.

